1. Field of the Invention
The invention pertains to longitudinally adjustable dunnage jack bar assemblies having a carriage slidably mounted on a jack bar longitudinally adjustable by an operating lever having power and lock pawls mounted thereon.
2. Description of the Related Art
Jacks and hoisting devices utilizing an elongated rigid toothed tube or bar having a movable carriage thereon wherein the carriage includes a pivoted operating lever controlling the movement of power and lock pawls have been known for many years. As illustrated in U.S. Pat. Nos. 1,175,211; 1,802,067; 1,974,491; 2,501,603 and 3,737,147, such devices have commonly been employed in the jack art, and bumper jacks using a toothed column were popularly employed as an automobile jack in the 1970's.
The principles existing with bumper jacks and the like have been utilized in the freight dunnage art wherein toothed jack bars extend between the sides of a van freight storage space having a carriage mounted thereon to which a van engaging abutment is mounted. By oscillating the carriage operating lever, the power and locking pawls mounted upon the operating lever translate the carriage on the jack bar to selectively adjust the length of the jack bar assembly permitting the jack bar to be tightly held in place by the van walls as the carriage is moved to lengthen the overall length of the jack bar assembly. As with automobile jacks, a dunnage jack bar assembly includes a release lever which permits the sequence of operation of the power and lock pawls to be reversed so that the length of the assembly can be retracted to permit the jack bar to be removed from its operative relationship to the van walls. While such operation of the reversing lever permits the carriage to be incrementally translated on the jack bar in a "retracting" direction, the spring biasing the locking lever toward the jack bar remains effective and prevents a rapid movement of the carriage on the jack bar in the retracting direction. A rapid translation of the carriage on the jack bar is only possible in extension direction.
In many instances, it is desirable to rapidly slide the carriage on the jack bar in either direction in order to permit a rapid initial jack bar assembly length adjustment prior to incrementally lengthening the jack bar assembly by oscillating the operating lever, but previously, such a release of the carriage as to permit rapid bi-directional movement on the jack bar has not been available.